The present invention relates to an optical displacement sensor. Such a sensor may be used in environments where a media in an optical path of the displacement sensor may undergo changes in refractive index and/or optical transmissivity.
U.S. Pat. No. 4,488,813 discloses an optical displacement sensor having two optical probes disposed at different distances X1 and X2 from a movable target. The distance to the target is calculated in accordance with X1=(X1-X2)E1/(E2-E1), where E1 and E2 are the intensities of the reflected light received at the first and second probes, respectively, and (X1-X2) is known from the sensor geometry.